Method and apparatus for monitoring control channel in unlicensed band

ABSTRACT

Provided are a method for monitoring a control channel in an unlicensed band and an apparatus using the same. In an unlicensed cell, a user equipment (UE) monitors a physical downlink control channel (PDCCH) having burst control information in a search space defined in a control region of a subframe. The control region comprises a plurality of control channel elements (CCEs) starting from an index 0, and the search space is defined only in, from among the plurality of CCEs, first four CCEs and first eight CCEs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/772,772, filed on May 1, 2018, which is theNational Stage filing under 35 U.S.C. 371 of International ApplicationNo. PCT/KR2016/012542, filed on Nov. 2, 2016, which claims the benefitof U.S. Provisional Applications No. 62/249,889 filed on Nov. 2, 2015,No. 62/256,142 filed on Nov. 17, 2015, No. 62/257,017 filed on Nov. 18,2015 and No. 62/288,393 filed on Jan. 28, 2016, the contents of whichare all hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method of monitoring a control channel in anunlicensed band, and an apparatus using the method.

Related Art

With the explosive increase in mobile data traffic in recent years, aservice provider has utilized a wireless local area network (WLAN) todistribute the data traffic. Since the WLAN uses an unlicensed band, theservice provider can address a demand for a significant amount of datawithout the cost of an additional frequency. However, there is a problemin that an interference phenomenon becomes serious due to a competitiveWLAN installation between the providers, quality of service (QoS) cannotbe guaranteed when there are many users, and mobility cannot besupported. As one of methods for compensating this, a long termevolution (LTE) service in the unlicensed band is emerged.

LTE in unlicensed spectrum (LTE-U) or licensed-assisted access using LTE(LAA) is a technique in which an LTE licensed band is used as an anchorto combine a licensed band and an unlicensed band by the use of carrieraggregation (CA). A user equipment (UE) first accesses a network in thelicensed band. A base station (BS) may offload traffic of the licensedband to the unlicensed band by combining the licensed band and theunlicensed band according to a situation.

The LTE-U may extend an advantage of LTE to the unlicensed band toprovide improved mobility, security, and communication quality, and mayincrease a throughput since the LTE has higher frequency efficiency thanthe legacy radio access technique.

Unlike the licensed band in which exclusive utilization is guaranteed,the unlicensed band is shared with various radio access techniques suchas the WLAN. Therefore, each communication node acquires a channel to beused in the unlicensed band in a contention-based manner, and this iscalled a carrier sense multiple access with collision avoidance(CSMA/CA). Each communication node must perform channel sensing beforetransmitting a signal to confirm whether a channel is idle, and this iscalled clear channel assessment (CCA).

Since a base station cannot guarantee an exclusive use of an unlicensedband, there is a need to design a control channel for a transmission ofcontrol information. Further, considering compatibility with theconventional LTE based control channel is also required.

SUMMARY OF THE INVENTION

The present invention provides a method for monitoring a control channelin an unlicensed band and an apparatus using the method.

In an aspect, a method for monitoring a control channel in an unlicensedband is provided. The method includes determining, by a user equipment(UE), a search space for monitoring a physical downlink control channel(PDCCH) having burst control information in a control region of asubframe in an unlicensed cell, and monitoring, by the UE, the PDCCH inthe search space of the subframe. The control region comprises aplurality of control channel elements (CCEs) starting from an index 0,and the search space is defined only in first 4 CCEs and first 8 CCEsamong the plurality of CCEs.

The burst control information may comprise information indicating aregion used for a transmission of a downlink (DL) channel in thesubframe.

In another aspect, an apparatus for monitoring a control channel in anunlicensed band includes a transceiver configured to transmit andreceive a radio signal, and a processor coupled to the transceiver. Theprocessor is configured to determine a search space for monitoring aphysical downlink control channel (PDCCH) having burst controlinformation in a control region of a subframe in an unlicensed cell, andmonitor the PDCCH in the search space of the subframe. The controlregion comprises a plurality of control channel elements (CCEs) startingfrom an index 0, and the search space is defined only in first 4 CCEsand first 8 CCEs among the plurality of CCEs.

A control channel can be monitored in an unlicensed band whilemaintaining compatibility with a control channel of the conventional3GPP LTE.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a long term evolution (LTE) service using anunlicensed band.

FIG. 2 shows a subframe structure in 3rd generation partnership project(3GPP) LTE.

FIG. 3 shows an example of monitoring a physical downlink shared channel(PDCCH) in 3GPP LTE.

FIG. 4 is a block diagram showing a physical hybrid-ARQ indicatorchannel (PHICH) in 3GPP LTE.

FIG. 5 shows burst transmission in an unlicensed band according to anembodiment of the present invention.

FIG. 6 shows a monitoring method according to an embodiment of thepresent invention.

FIG. 7 is a block diagram showing a wireless communication system forimplementing an embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A wireless device may be fixed or mobile, and may be referred to asanother terminology, such as a user equipment (UE), a mobile station(MS), a mobile terminal (MT), a user terminal (UT), a subscriber station(SS), a personal digital assistant (PDA), a wireless modem, a handhelddevice, etc. The wireless device may also be a device supporting onlydata communication such as a machine-type communication (MTC) device.

A base station (BS) is generally a fixed station that communicates withthe wireless device, and may be referred to as another terminology, suchas an evolved-NodeB (eNB), a base transceiver system (BTS), an accesspoint, etc.

Hereinafter, it is described that the present invention is appliedaccording to a 3^(rd) generation partnership project (3GPP) long termevolution (LTE) based on 3GPP technical specification (TS). However,this is for exemplary purposes only, and thus the present invention isalso applicable to various wireless communication networks.

In a carrier aggregation (CA) environment or a dual connectivityenvironment, the wireless device may be served by a plurality of servingcells. Each serving cell may be defined with a downlink (DL) componentcarrier (CC) or a pair of a DL CC and an uplink (UL) CC.

The serving cell may be classified into a primary cell and a secondarycell. The primary cell operates at a primary frequency, and is a celldesignated as the primary cell when an initial network entry process isperformed or when a network re-entry process starts or in a handoverprocess. The primary cell is also called a reference cell. The secondarycell operates at a secondary frequency. The secondary cell may beconfigured after an RRC connection is established, and may be used toprovide an additional radio resource. At least one primary cell isconfigured always. The secondary cell may be added/modified/released byusing higher-layer signaling (e.g., a radio resource control (RRC)message).

A cell index (CI) of the primary cell may be fixed. For example, alowest CI may be designated as a CI of the primary cell. It is assumedhereinafter that the CI of the primary cell is 0 and a CI of thesecondary cell is allocated sequentially starting from 1.

FIG. 1 shows an example of an LTE service using an unlicensed band.

A wireless device 130 establishes a connection with a 1^(st) BS 110, andreceives a service through a licensed band. For traffic offloading, thewireless device 130 may receive a service through an unlicensed bandwith respect to a 2^(nd) BS 120.

The 1^(st) BS 110 is a BS supporting an LTE system, whereas the 2^(nd)BS 120 may also support other communication protocols such as a wirelesslocal area network (WLAN) in addition to LTE. The 1^(st) BS 110 and the2^(nd) BS 120 may be associated with a carrier aggregation (CA)environment, and a specific cell of the 1^(st) BS 110 may be a primarycell. Alternatively, the 1^(st) BS 110 and the 2^(nd) BS 120 may beassociated with a dual connectivity environment, and a specific cell ofthe 1^(st) BS 110 may be a primary cell. In general, the 1^(st) BS 110having the primary cell has wider coverage than the 2^(nd) BS 120. The1^(st) BS 110 may be called a macro cell. The 2^(nd) BS 120 may becalled a small cell, a femto cell, or a micro cell. The 1^(st) BS 110may operate the primary cell and zero or more secondary cells. The2^(nd) BS 120 may operate one or more secondary cells. The secondarycell may be activated/deactivated by an indication of the primary cell.

The above description is for exemplary purposes only. The 1^(st) BS 110may correspond to the primary cell, and the 2^(nd) BS 120 may correspondto the secondary cell, so that the cell can be managed by one BS.

The licensed band is a band in which an exclusive use is guaranteed to aspecific communication protocol or a specific provider.

The unlicensed band is a band in which various communication protocolscoexist and a shared use is guaranteed. The unlicensed band may include2.5 GHz and/or 5 GHz band used in a WLAN.

It is assumed in the unlicensed band that a channel is occupiedbasically through contention between respective communication nodes.Therefore, in communication in the unlicensed band, it is required toconfirm that signal transmission is not achieved by other communicationnodes by performing channel sensing. For convenience, this is called alisten before talk (LBT), and if it is determined that signaltransmission is not achieved by other communication nodes, this case isdefined as confirmation of clear channel assessment (CCA).

The LBT must be performed preferentially in order for a BS or wirelessdevice of an LTE system to have access to a channel in the unlicensedband. Further, when the BS or wireless device of the LTE systemtransmits a signal, an interference problem may occur since othercommunication nodes such as the WLAN or the like also perform the LBT.For example, in the WLAN, a CCA threshold is defined as −62 dBm as to anon-WLAN signal and is defined as −82 dBm as to a WLAN signal. Thismeans that interference may occur in an LTE signal due to other WLANdevices when the LTE signal is received with power less than or equal to−62 dBm.

Hereinafter, when it is said that ‘LBT is performed’ or ‘CCA isperformed’, it implies that whether a channel is idle or is used byanother node is confirmed first and thereafter the channel is accessed.

Hereinafter, the LTE and the WLAN are described for example as acommunication protocol used in the unlicensed band. This is forexemplary purposes only, and thus it may also be said that a 1^(st)communication protocol and a 2^(nd) communication protocol are used inthe unlicensed band. A BS supports the LTE. A UE is a device supportingthe LTE.

Hereinafter, although it is described that downlink (DL) transmission isbased on transmission performed by a BS and uplink (UL) transmission isbased on transmission performed by a UE, the DL transmission and the ULtransmission may also be performed by a transmission node or node groupin a wireless network. The UE may imply an individual node which existsfor each user, and the BS may imply a central node fortransmitting/receiving and controlling data for a plurality ofindividual nodes. From this perspective, the term ‘BS’ may be replacedwith a DL node, and the term ‘UE’ may be replaced with a UL node.

A cell operating in an unlicensed band is referred to as ‘unlicensedcell’ and a cell operating in a licensed band is referred to as‘licensed cell’. For clarity, it is assumed that a licensed cell is aprimary cell and an unlicensed cell is a secondary cell.

FIG. 2 shows a subframe structure in 3GPP LTE.

A radio frame includes 10 subframes indexed with 0 to 9. One subframeincludes 2 consecutive slots. A time required for transmitting onesubframe is defined as a transmission time interval (TTI). For example,one subframe may have a length of 1 millisecond (ms), and one slot mayhave a length of 0.5 ms.

One slot may include a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in a time domain. Since the 3GPP LTE-A usesorthogonal frequency division multiple access (OFDMA) in a downlink(DL), the OFDM symbol is only for expressing one symbol period in thetime domain, and there is no limitation in multiple access schemes orterminologies. For example, the OFDM symbol may also be referred to asanother terminology such as a single carrier frequency division multipleaccess (SC-FDMA) symbol, a symbol period, etc.

Although it is described that one subframe includes 14 OFDM symbols forexample, the number of OFDM symbols included in one slot may varydepending on a length of a cyclic prefix (CP). According to 3GPP LTE-A,in case of a normal CP, one subframe includes 14 OFDM symbols, and incase of an extended CP, one subframe includes 12 OFDM symbols.

A resource block (RB) is a resource allocation unit and includes aplurality of subcarriers in one slot. For example, if one slot includes7 OFDM symbols in a time domain and the RB includes 12 subcarriers in afrequency domain, one RB can include 7×12 resource elements (REs).

Physical channels in 3GPP LTE are classified into a downlink (DL)physical channel and a uplink (UL) physical channel. DL physicalchannels include a physical downlink control channel (PDCCH), a physicalcontrol format indicator channel (PCFICH), a physical hybrid-ARQindicator channel (PHICH), and a physical downlink shared channel(PDSCH).

The PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an UL hybrid automaticrepeat request (HARQ). The ACK/NACK signal for UL data on a PUSCHtransmitted by the wireless device is transmitted on the PHICH.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). The DCI may include resourceallocation of the PDSCH (this is referred to as a downlink (DL) grant),resource allocation of a PUSCH (this is referred to as an uplink (UL)grant), a set of transmit power control commands for individual UEs inany UE group, and/or activation of a voice over Internet protocol(VoIP).

In 3GPP LTE/LTE-A, transmission of a DL transport block is performed ina pair of the PDCCH and the PDSCH. Transmission of a UL transport blockis performed in a pair of the PDCCH and the PUSCH. For example, thewireless device receives the DL transport block on a PDSCH indicated bythe PDCCH. The wireless device receives a DL resource assignment on thePDCCH by monitoring the PDCCH in a DL subframe. The wireless devicereceives the DL transport block on a PDSCH indicated by the DL resourceassignment.

FIG. 3 shows an example of monitoring a PDCCH in 3GPP LTE.

The 3GPP LTE uses blind decoding for PDCCH detection. The blind decodingis a scheme in which a desired identifier is de-masked from a CRC of areceived PDCCH (referred to as a candidate PDCCH) to determine whetherthe PDCCH is its own control channel by performing CRC error checking. Awireless device cannot know about a specific position in a controlregion in which its PDCCH is transmitted and about a specific CCEaggregation or DCI format used for PDCCH transmission.

A control region in a subframe includes a plurality of control channelelements (CCEs). The CCE is a logical allocation unit used to providethe PDCCH with a coding rate depending on a radio channel state, andcorresponds to a plurality of resource element groups (REGs). The REGincludes a plurality of REs. According to an association relation of thenumber of CCEs and the coding rate provided by the CCEs, a PDCCH formatand a possible number of bits of the PDCCH are determined. One REGincludes 4 REs. One CCE includes 9 REGs. The number of CCEs used toconfigure one PDCCH may be selected from a set {1, 2, 4, 8}. Eachelement of the set {1, 2, 4, 8} is referred to as a CCE aggregationlevel.

A plurality of PDCCHs can be transmitted in one subframe. The wirelessdevice monitors the plurality of PDCCHs in every subframe. Monitoring isan operation of attempting PDCCH decoding by the wireless deviceaccording to a format of the monitored PDCCH.

The 3GPP LTE uses a search space to reduce a load of blind decoding. Thesearch space can also be called a monitoring set of a CCE for the PDCCH.The wireless device monitors the PDCCH in the search space.

The search space is classified into a common search space and aUE-specific search space. The common search space is a space forsearching for a PDCCH having common control information and consists of16 CCEs indexed with 0 to 15. The common search space supports a PDCCHhaving a CCE aggregation level of {4, 8}. However, a PDCCH (e.g., DCIformats 0, 1A) for carrying UE-specific information can also betransmitted in the common search space. The UE-specific search spacesupports a PDCCH having a CCE aggregation level of {1, 2, 4, 8}.

In a CCE aggregation level L∈{1,2,3,4}, a search space S^((L)) _(k) isdefined as a set of PDCCH candidates. A CCE corresponding to a PDCCHcandidate m of the search space S^((L)) _(k) is given by Equation 1below.L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Herein, i=0, 1, . . . , L−1, and N_(CCE,k) denotes the total number ofCCEs that can be used for PDCCH transmission in a control region of asubframe k. The control region includes a set of CCEs numbered from 0 toN_(CCE,k-1). If a carrier indicator field (CIF) is set to theUE-specific search space, m′=m+M^((L))n_(cif). Herein, n_(cif) is avalue of the CIF. If the CIF is not set to the UE-specific search space,m′=m. m=0, . . . , M^((L))−. M^((L)) denotes the number of PDCCHcandidates in a CCE aggregation level L of a given search space.

In a common search space, Y_(k) is set to 0 with respect to twoaggregation levels L=4 and L=8. In a UE-specific search space of theaggregation level L, a variable Y_(k) is defined by Equation 2 below.Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, A=39827, D=65537, k=floor(n_(s)/2), and n_(s)denotes a slot number in a radio frame.

FIG. 4 shows a structure of a PHICH in 3GPP LTE.

One PHICH carries only 1-bit ACK/NACK corresponding to a PUSCH for oneUE, that is, corresponding to a single stream.

In step S310, the 1-bit ACK/NACK is coded into 3 bits by using arepetition code having a code rate of 1/3.

In step S320, the coded ACK/NACK is modulated using binary phase shiftkeying (BPSK) to generate 3 modulation symbols.

In step S330, the modulation symbols are spread by using an orthogonalsequence. A spreading factor (SF) is N^(PHICH) _(SF)=4 in a normal CPcase, and is N^(PHICH) _(SF)=2 in an extended CP case. The number oforthogonal sequences used in the spreading is N^(PHICH) _(SF)*2 to applyI/Q multiplexing. PHICHs which are spread by using N^(PHICH) _(SF)*2orthogonal sequences can be defined as one PHICH group.

In step S340, layer mapping is performed on the spread symbols.

In step S350, the layer-mapped symbols are transmitted by being mappedto resources.

A plurality of PHICHs mapped to resource elements of the same setconstitute a PHICH group. Each PHICH included in the PHICH group isidentified by a different orthogonal sequence. In the FDD system,N^(group) _(PHICH), i.e., the number of PHICH groups, is constant in allsubframes, and can be determined by Equation 3 below.

$\begin{matrix}{N_{PHICH}^{group} = \left\{ \begin{matrix}\left\lceil {N_{g}\left( {N_{RB}^{DL}/8} \right)} \right\rceil & {{for}\mspace{14mu}{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}} \\{2 \cdot \left\lceil {N_{g}\left( {N_{RB}^{DL}/8} \right)} \right\rceil} & {{or}\mspace{14mu}{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Herein, Ng denotes a parameter transmitted through a physical broadcastchannel (PBCH), where NgE {1/6,1/2,1,2}. N^(DL) _(RB) denotes the numberof DL RBs.

The wireless device identifies a PHICH resource by using an index pair(n^(group) _(PHICH), n^(seq) _(PHICH)) used by the PHICH. A PHICH groupindex n^(goup) _(PHICH) has a value in the range of 0 to N^(group)_(PHICH)−1. An orthogonal sequence index n^(seq) _(PHICH) denotes anindex of an orthogonal sequence. An index pair (n^(group) _(PHICH),n^(seci) _(PHICH)) is obtained according to Equation 4 below.n _(PHICH) ^(group)=(I _(PRB_RA) +n _(DMRS))mod N _(PHICH) ^(group) +I_(PHICH) N _(PHICH) ^(group)n_(PHCICH) ^(seq)=(└I _(PRB_RA) /N _(PHICH) ^(group) ┘+n _(DMRS))mod 2N_(SF) ^(PHICH)   [Equation 4]

Herein, n_(DMRS) denotes a cyclic shift of a demodulation referencesignal (DMRS) within the most recent UL grant for a transport blockrelated to corresponding PUSCH transmission. The DMRS is an RS used forPUSCH transmission. N^(PHICH) _(SF) denotes an SF size of an orthogonalsequence used in PHICH modulation. I^(lowest_index) _(PRB_RA) denotesthe smallest PRB index in a 1^(st) slot of corresponding PUSCHtransmission. I_(PHICH) is 0 or 1.

FIG. 5 shows burst transmission in an unlicensed band according to anembodiment of the present invention.

A burst refers to a packet transmitted after CCA is complete, and may betransmitted in one or more consecutive subframes. This may imply thatthe burst is transmitted on one or more PUSCHs. At the start of theburst, a reservation signal may be transmitted for channel occupation,burst start detection, and time/frequency synchronization.

In the existing 3GPP LTE, the start of DL/UL data transmission islimited to a subframe boundary. However, if data transmission starttiming is limited to an OFDM symbol boundary or a subframe boundary inan unlicensed band, another transmitting node may start signaltransmission between any time at which a transmission node identifiesCCA and a data transmission start time, which may lead to a failure inchannel occupation. To prevent this, DL transmission may startimmediately after identifying the CCA or within a specific time, ratherthan the subframe boundary. A case where burst transmission starts inthe middle of a subframe is called a partial start subframe. A casewhere burst transmission ends in the middle of the subframe is called apartial end subframe.

A BS may transmit burst control information in each subframe and/or asubframe in which CCA is successful. The burst control information mayinclude a length of each subframe in a burst, a presence/absence of areference signal (RS) for measuring channel state information (CSI), apresence/absence of a cell-specific reference signal (CRS), or the like.The burst control information may include information regarding asubframe configuration for a previous subframe and/or a currentsubframe. The burst control information may include informationregarding a duration in which the burst is transmitted (or the number ofOFDM symbols for transmitting the burst) in the subframe. The burstcontrol information may include information regarding a duration inwhich a DL channel (e.g., PDCCH, PDSCH, etc.) is transmitted (or thenumber of OFDM symbols for transmitting a DL channel) in the subframe.

The burst control information transmitted in a subframe n may indicate asubframe configuration in the subframe n. Alternatively, the burstcontrol information transmitted in the subframe n may indicate asubframe configuration in a subframe n+1. Alternatively, the burstcontrol information transmitted in both the subframe n and the subframen+1 may indicate a subframe configuration in the subframe n+1.

The burst control information may be transmitted in a licensed cell oran unlicensed cell. The burst control information may be transmitted ina primary cell. Alternatively, the burst control information may betransmitted in an unlicensed band in which a burst is transmitted.

Hereinafter, a structure of a control channel for carrying burst controlinformation in an unlicensed band is proposed.

The Use of PHICH Structure

As described above, in 3GPP LTE, a payload of a PHICH is a 1-bit DL HARQACK/NACK. The 1-bit ACK/NACK may be coded into 3 bits by using arepetition code having a code rate of 1/3, and is modulated based onBPSK.

According to the proposed embodiment, burst control information is thepayload of the PHICH. In order to transmit the burst control informationthrough the PHICH, the burst control information may be encoded by usinga Reed-Muller (RM) code as follows.

$\begin{matrix}{b_{i} = {\sum\limits_{n = 0}^{A - 1}{\left( {a_{n} \cdot M_{i,n}} \right){mod}\; 2}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

b_(i) is an encoded bit. a_(n) is a bit of burst control information. Ais the number of bits of the burst control information. i=0, . . . , I,where I is the number of encoded bits. M_(i,n) is a basis sequence forthe RM code.

If I=32 and A=11, then M_(i,n) may be as shown in the following table.This is called a length-32 RM code.

TABLE 1 i M_(i,0) M_(i,1) M_(i,2) M_(i,3) M_(i,4) M_(i,5) M_(i,6)M_(i,7) M_(i,8) M_(i,9) M_(i,10) 0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 00 0 1 1 2 1 0 0 1 0 0 1 0 1 1 1 3 1 0 1 1 0 0 0 0 1 0 1 4 1 1 1 1 0 0 01 0 0 1 5 1 1 0 0 1 0 1 1 1 0 1 6 1 0 1 0 1 0 1 0 1 1 1 7 1 0 0 1 1 0 01 1 0 1 8 1 1 0 1 1 0 0 1 0 1 1 9 1 0 1 1 1 0 1 0 0 1 1 10 1 0 1 0 0 1 11 0 1 1 11 1 1 1 0 0 1 1 0 1 0 1 12 1 0 0 1 0 1 0 1 1 1 1 13 1 1 0 1 0 10 1 0 1 1 14 1 0 0 0 1 1 0 1 0 0 1 15 1 1 0 0 1 1 1 1 0 1 1 16 1 1 1 0 11 1 0 0 1 0 17 1 0 0 1 1 1 0 0 1 0 0 18 1 1 0 1 1 1 1 1 0 0 0 19 1 0 0 00 1 1 0 0 0 0 20 1 0 1 0 0 0 1 0 0 0 1 21 1 1 0 1 0 0 0 0 0 1 1 22 1 0 00 1 0 0 1 1 0 1 23 1 1 1 0 1 0 0 0 1 1 1 24 1 1 1 1 1 0 1 1 1 1 0 25 1 10 0 0 1 1 1 0 0 1 26 1 0 1 1 0 1 0 0 1 1 0 27 1 1 1 1 0 1 0 1 1 1 0 28 10 1 0 1 1 1 0 1 0 0 29 1 0 1 1 1 1 1 1 1 0 0 30 1 1 1 1 1 1 1 1 1 1 1 311 0 0 0 0 0 0 0 0 0 0

If I=20 and A=13, then M_(i,n) may be as shown in the following table.This is called a length-20 RM code.

TABLE 2 i M_(i,0) M_(i,1) M_(i,2) M_(i,3) M_(i,4) M_(i,5) M_(i,6)M_(i,7) M_(i,8) M_(i,9) M_(i,10) M_(i,11) M_(i,12) 0 1 1 0 0 0 0 0 0 0 01 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 0 2 1 0 0 1 0 0 1 0 1 1 1 1 1 3 1 0 1 10 0 0 0 1 0 1 1 1 4 1 1 1 1 0 0 0 1 0 0 1 1 1 5 1 1 0 0 1 0 1 1 1 0 1 11 6 1 0 1 0 1 0 1 0 1 1 1 1 1 7 1 0 0 1 1 0 0 1 1 0 1 1 1 8 1 1 0 1 1 00 1 0 1 1 1 1 9 1 0 1 1 1 0 1 0 0 1 1 1 1 10 1 0 1 0 0 1 1 1 0 1 1 1 111 1 1 1 0 0 1 1 0 1 0 1 1 1 12 1 0 0 1 0 1 0 1 1 1 1 1 1 13 1 1 0 1 0 10 1 0 1 1 1 1 14 1 0 0 0 1 1 0 1 0 0 1 0 1 15 1 1 0 0 1 1 1 1 0 1 1 0 116 1 1 1 0 1 1 1 0 0 1 0 1 1 17 1 0 0 1 1 1 0 0 1 0 0 1 1 18 1 1 0 1 1 11 1 0 0 0 0 0 19 1 0 0 0 0 1 1 0 0 0 0 0 0

The burst control information may be encoded by repeating or truncatingthe length-32 RM code or the length-20 RM code. There is no limitationin the length of the RM code, and the length-32 or length-48 RM code maybe used.

M PHICHs may be used to transmit the encoded burst control informationhaving a length A.

In a first embodiment, one encoded bit may be transmitted for eachPHICH. In this case, M=A. When L PHICHs are used for each PHICH group,the burst control information may be transmitted by using ceiling(M/L)PHICH groups. For example, if L=8, then 3, 3, 4, and 6 PHICH groups maybe used respectively for M=20, 24, 32, and 48. Alternatively, when usinga plurality of PHICHs belonging to one PHICH group, transmit (TX) powermay be significantly concentrated in a frequency resource used by thePHICH, and thus the TX power may be significantly unbalanced in afrequency domain. Therefore, more PHICH groups may be used by applyingonly a part of orthogonal sequence and I/Q component combinations. Only1, 2, or 4 orthogonal sequences in the PHICH group may be used (L=1, 2,4). Only the I/Q components in the PHICH group may be used (L=2).

In a second embodiment, one encoded bit may be transmitted per REGbelonging to each PHICH. Since 3 REGs are used for each PHICH,M=ceiling(A/3). When L PHICHs are used for each PHICH group, the burstcontrol information may be transmitted by using ceiling(M/L) PHICHgroups. For example, if L=8, then 1, 1, 2, and 2 PHICH groups may beused respectively for M=20, 24, 32, and 48. Alternatively, when using aplurality of PHICHs belonging to one PHICH group, TX power may besignificantly concentrated in a frequency resource used by the PHICH,and thus the TX power may be significantly unbalanced in a frequencydomain. Therefore, more PHICH groups may be used by applying only a partof orthogonal sequence and I/Q component combinations. Only 1, 2, or 4orthogonal sequences in the PHICH group may be used (L=1, 2, 4). Onlythe I/Q components in the PHICH group may be used (L=2).

In a third embodiment, one encoded bit may be transmitted per REGconstituting the PHICH.

In a fourth embodiment, two encoded bits may be transmitted using QPSKmodulation in the first to third embodiments.

In the first to fourth embodiments, a bit having a high priority inburst control information may be assigned to a most significant bit(MSB). For example, if the burst control information includes higherpriority information (information required for (E)PDCCH/PDSCH reception,a subframe configuration, a CRS port/symbol count, etc.), decodingperformance of corresponding information may be improved by assigningthe high priority information to the MSB.

A different encoding scheme may be applied depending on the number ofbits of the burst control information transmitted through the PHICH. Ifthe burst control information is 1 bit, repetition coding is applied. Ifthe burst control information is 2 bits, the following simplex coding isapplied.

TABLE 3 2-bit burst control information encoded bit 00 011 01 101 10 11011 000

If the burst control information is at least 3 bits, the aforementionedRM code is applied. Burst control information which is encodedindependently may be transmitted through different PHICHs and/ordifferent PHICH groups.

Tail-biting convolutional coding may be applied to the burst controlinformation transmitted through the PHICH. To reduce an amount of PHICHresources used per subframe, CRC may be omitted, or only one parity bitmay be added. Alternatively, CRC of 8 bits or less may be added.

When an encoded bit is transmitted per RE as in the third embodiment, inorder to prevent an error of corresponding bits from occurring due toadjacent REs experiencing the same fading channel, block interleavingmay be applied before an encoded bit is mapped to each RE. One blockinterleaving may be applied for each PHICH group or for all PHICHgroups. The block interleaving may include operations of writing aninput bit in a column-wise manner and generating an output bit in arow-wise manner after being subjected to column permutation. A columnand a row may be applied in a reverse order. If the column or row of theinterleaving is a multiple of 4 or if the number of PHICH groups is amultiple of 4, a block interleaving size may be determined such that thecolumn or the row is not the multiple of 4 in order to prevent frombeing re-mapped to the same REG. Alternatively, the encoded bit may bemapped to the RE by applying the interleaving between a plurality ofPHICH groups and a plurality of adjacent PHICH REGs.

An OFDM symbol on which the PHICH having the burst control informationis transmitted may be limited to a first OFDM symbol of a subframe.PHICH mapping may conform to a case where a PHICH duration is 1 OFDMsymbol. If a control region in the subframe is set to 2 OFDM symbols,the PHICH may be limitedly transmitted on only 2 OFDM symbols. When thePHICH duration is set to an extended PHICH duration, the PHICH mayalways be transmitted on 2 OFDM symbols.

The number of OFDM symbols on which the PHICH is transmitted may bedetermined according to a duration of a non-MBSFN region of amulticast-broadcast single-frequency network (MBSFN) subframe. If thenon-MBSFN region uses one OFDM symbol, the number of OFDM symbols onwhich the PHICH is transmitted may always be one in all subframes. Ifthe non-MBSFN region uses 2 OFDM symbols, the number of OFDM symbols towhich the PHICH is transmitted may always be 2 in all subframes.

In the existing 3GPP LTE, when a BS supports 4 transmit (TX) diversity,antenna diversity is obtained by mapping different PHICH groups todifferent antenna pairs. When an encoded bit is transmitted per PHICHRE, the antenna diversity may be obtained in such a manner that anadjacent RE pair is mapped to a different antenna pair.

The PHICH having the burst control information may be transmitted onlyin a specific subframe. RE mapping of the PDCCH or the PDSCH variesdepending on whether the UE transmits the PHICH. This is to prevent anerror from occurring in reception of another channel when the UEincorrectly detects whether the PHICH is transmitted. REs to be occupiedby the PHICH irrespective of whether the PHICH is transmitted may not beused in transmission of the PDCCH or the PDSCH. Alternatively, the UEmay detect whether the PHICH is transmitted in each subframe (using CRCcheck or other conditions), and according to a result thereof, maydetermine whether the PDCCH or the PDSCH is mapped to up to an RE to beused by the PHICH.

An amount of a PHICH resource having the burst control information maybe determined as follows. The amount of the PHICH resource may be set to0 in the following methods.

In a first embodiment, the BS may deliver the amount of the PHICHresource to the UE through RRC signaling. The amount of the PHICHresource may be expressed by the number of PHICHs, the number of PHICHgroups, or the number of REGs constituting the PHICH.

In a second embodiment, the BS may deliver the number of bits of theburst control information or the number of encoded bits of the burstcontrol information to the UE through the RRC signaling. The UE maydetermine the amount of the PHICH resource through the number ofcorresponding bits.

The Use of PDCCH Structure

In the 3GPP LTE system, burst control information may be transmitted ona PDCCH or EPDCCH used in DCI transmission. Hereinafter, the PDDCH orEPDCCH for transmitting the burst control information is referred to asa b-PDCCH.

The number of bits of burst control information to be transmitted on theb-PDCCH may be predetermined, or may be informed by a BS to a UE throughRRC signaling. A DCI format for the burst control information (this iscalled a burst DCI format) may be separately determined or the existingDCI format may be re-used. When the number of bits of the burst controlinformation is denoted by A and the number of DCI formats is denoted byZ, then Z>=A. Although the UE decodes the Z-bit burst DCI format, only Abits among them are used as actual burst control information. Z-A bitsare reserved bits and thus are not used. For example, if the burst DCIformat has the same number of bits as the DCI format 1C, the Z-A bitsare the reserved bits.

FIG. 6 shows a monitoring method according to an embodiment of thepresent invention.

In step S610, a search space for monitoring burst control information isdetermined in a control region of a subframe of an unlicensed cell.

In step S620, a b-PDCCH is monitored in the search space. A specificRNTI for the b-PDCCH may be defined, and is referred to as b-RNTI. A UEidentifies a CRC error of a PDCCH candidate by using the b-RNTI in thesearch space. If the error is not detected, a corresponding PDCCHcandidate is detected as the b-PDCCH, and the burst control informationis decoded.

A CCE aggregation level for configuring the b-PDCCH may be set by RRCsignaling. The b-PDCCH may be monitored using a specific aggregationlevel (L=4 or 8).

The search space for the b-PDCCH may be defined. Alternatively, theb-PDCCH may be monitored in a common search space. More specifically, alocation of the PDCCH in which the b-PDCCH is to be monitored may bepredetermined also in the search space. For example, the UE may monitorthe b-PDCCH only in a first PDCCH candidate in the common search space.For example, it is assumed that a CCE index starts from 0, and thesearch space starts from a CCE having the CCE index 0. If L=4, the UEmonitors the b-PDCCH in PDCCH candidates corresponding to CCE indices 0,1, 2, and 3. If L=8, the UE monitors the b-PDCCH in PDCCH candidatescorresponding to CCE indices 0, 1, 2, 3, 4, 5, 6, and 7. The UE maydamask CRC of a corresponding PDCCH candidate, and if there is no CRCerror, it may be recognized as the b-PDCCH. A CCE aggregation level andthe number of PDCCH candidates may be limited for the monitoring of theb-PDCCH to decrease an overhead based on blind decoding.

The BS may inform the UE of a search space for monitoring the b-PDCCHand/or a location of the PDCCH candidate.

The BS may inform the UE of configuration information regarding thesearch space for monitoring the b-PDCCH. The configuration informationmay include a start point of the search space and/or the number of PDCCHcandidates.

Since the burst control information has fewer bits than typical DCI, CRCof 8 bits or less may be used.

Information indicating an MBSFN subframe or information indicatingwhether it is a partial subframe may be masked in the CRC of theb-PDCCH.

In the 3GPP LTE, a PCFICH uses 4 REGs (one REG includes 4 REs adjacentto the maximum extent possible on a frequency axis in OFDM symbol). Ifthe burst control information is 2 bits, the burst control informationmay be transmitted by using simplex coding as shown in Table 3. If theburst control information is greater than 2 bits, it may be transmittedon a plurality of PCFICHs. The plurality of PCFICHs may be transmittedon one OFDM symbol, or may be transmitted on different OFDM symbols. Theburst control information may be encoded using a simplex code or an RMcode.

A control region is a region in which a PDCCH/PHICH/PCFICH istransmitted in the subframe. The control region includes up to first 3OFDM symbols of the subframe. In the 3GPP LTE, the UE may know aduration of the control region through the PCFICH transmitted on a firstOFDM symbol of each subframe. In cross-carrier scheduling in which thePDCCH is transmitted in a first cell and the PDSCH is transmitted in asecond cell, the UE does not detect the PDCCH or PHICH in the secondcell and the duration of the control region is set through RRCsignaling. If the second cell is an unlicensed cell, there is a need todefine a control region of the unlicensed cell to receive the controlchannel (PDCCH/PHICH) used in transmission of burst control information.

In the cross-carrier scheduling, the UE may assume previous symbols ofan OFDM symbol configured to transmit PDSCH transmission in eachsubframe as the control region. It is assumed that PDSCH transmission isconfigured to start from a K^(th) OFDM symbol in the subframe. The UEmay assume that the control region is from a first OFDM symbol to anR^(th) OFDM symbol (R>k). Alternatively, the BS may provide the UE withinformation regarding the control region used by the control channelused in transmission of the burst control information. In the MBSFNsubframe, an 01-DM symbol configured to a non-MBSFN region may beassumed as the control region.

If the UE detects a decoding error of the burst control information ordetects a discrepancy between the burst control information and DLscheduling information in the CRC check or other methods, the followingactions may be taken.

(1) The UE discards reception of a corresponding subframe or acorresponding burst.

(2) The UE ignores corresponding burst control information and conformsto the DL scheduling information.

(3) The UE attempts to perform reception according to a configurationpredetermined in a corresponding subframe or a corresponding burst. Thepredetermined configuration may include a configuration for anMBSFN/non-MBSFN subframe, a configuration for a subframe length, and aconfiguration for whether an RS exists for CSI measurement. For example,the UE may assume that the corresponding subframe is the non-MBSFNsubframe and is not a partial subframe, and that all RSs configured forCSI measurement are present.

Now, transmission of reference signal (RS) TX power will be described.TX power of an RS (CRS, CSI-RS, DRS, etc.) in an unlicensed ell may varyon a burst basis. Burst control information may include informationregarding the RS TX power. An RS transmitted periodically for DLsynchronization such as a discovery RS (DRS) may use TX power which isfixed for a long period of time instead of changing the TX powerdynamically. The TX power may be given by RRC signaling. That is, TXpower of the CRS/CSI-RS constituting the DRS may be delivered to the UEby RRC signaling. This may be delivered to the UE in such a manner thatCRS TX power delivered by RRC signaling is limitedly applied only to theCRS for the DRS. A relationship between CRS TX power and PDSCH TX powerand a relationship with CSI-RS TX power may be limitedly applied only toa subframe in which the DRS is transmitted or may be applied to allsubframes. The BS may inform the UE of whether the CRS TX power islimited in a subframe in which the DRS is transmitted, through the RRCsignaling. The UE may calculate a path loss between the BS and the UE byusing the relationship between receive (RX) power of the RS transmittedthrough the DRS and RS TX power determined by the RRC signaling, and mayutilize it to compensate for the path loss in UL TX power.

FIG. 7 is a block diagram showing a wireless communication system forimplementing an embodiment of the present invention.

A wireless device 50 includes a processor 51, a memory 52, and a radiofrequency (RF) unit 53. The memory 52 is coupled to the processor 51,and stores various instructions executed by the processor 51. The RFunit 53 is coupled to the processor 51, and transmits and/or receives aradio signal. The processor 51 implements the proposed functions,procedures, and/or methods. In the aforementioned embodiment, anoperation of the wireless device may be implemented by the processor 51.When the aforementioned embodiment is implemented with a softwareinstruction, the instruction may be stored in the memory 52, and may beexecuted by the processor 51 to perform the aforementioned operation.

A BS 60 includes a processor 61, a memory 62, and an RF unit 63. The BS60 may operate in a licensed band and/or an unlicensed band. The memory62 is coupled to the processor 61, and stores various instructionsexecuted by the processor 61. The RF unit 63 is coupled to the processor61, and transmits and/or receives a radio signal. The processor 61implements the proposed functions, procedures, and/or methods. In theaforementioned embodiment, an operation of the BS may be implemented bythe processor 61.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

In the above exemplary systems, although the methods have been describedon the basis of the flowcharts using a series of the steps or blocks,the present invention is not limited to the sequence of the steps, andsome of the steps may be performed at different sequences from theremaining steps or may be performed simultaneously with the remainingsteps. Furthermore, those skilled in the art will understand that thesteps shown in the flowcharts are not exclusive and may include othersteps or one or more steps of the flowcharts may be deleted withoutaffecting the scope of the present invention.

What is claimed is:
 1. A method for a wireless communication system, the method comprising: detecting, by a user equipment (UE), a physical downlink control channel (PDCCH) in a search space of a first subframe of a licensed-assisted access (LAA) secondary cell; and acquiring control information based on the detected PDCCH, the control information that includes information on a subframe configuration for the first subframe and a second subframe of the LAA secondary cell, the second subframe being a next subframe of the first subframe, wherein the first subframe includes a plurality of control channel elements (CCEs), and wherein the search space is defined in a single PDCCH candidate given by first N CCEs from the plurality of CCEs in the first subframe at each aggregation level, where N denotes an aggregation level.
 2. The method of claim 1, wherein the search space is defined in at least one of a first PDCCH candidate at an aggregation level 4 and a second PDCCH candidate at an aggregation level 8, the first PDCCH candidate given by four CCEs numbered 0, 1, 2, 3, the second PDCCH candidate given by eight CCEs numbered 0, 1, 2, 3, 4, 5, 6,
 7. 3. The method of claim 1, wherein the subframe configuration for the first subframe and the second subframe indicates a number of orthogonal frequency division multiplexing (OFDM) symbols used for transmission of downlink channels in the first subframe and the second subframe.
 4. The method of claim 1, wherein a radio network temporary identifier (RNTI) is masked to a cyclic redundancy check (CRC) of the control information.
 5. The method of claim 1, wherein the control information is common control information common to all UE's in the LAA secondary cell.
 6. The method of claim 1, further comprising: activating, by the UE, the LAA secondary cell by receiving an instruction from a primary cell.
 7. An apparatus for a wireless communication system, the apparatus comprising: a processor; and a memory operatively coupled with the processor and storing instructions that when executed by the processor cause the apparatus to: detect a physical downlink control channel (PDCCH) in a search space of a first subframe of a licensed-assisted access (LAA) secondary cell; and acquire control information based on the detected PDCCH, the control information that includes information on a subframe configuration for the first subframe and a second subframe of the LAA secondary cell, the second subframe being a next subframe of the first subframe, wherein the first subframe includes a plurality of control channel elements (CCEs), and wherein the search space is defined in a single PDCCH candidate given by first N CCEs from the plurality of CCEs in the first subframe at each aggregation level, where N denotes an aggregation level.
 8. The apparatus of claim 7, wherein the search space is defined in at least one of a first PDCCH candidate at an aggregation level 4 and a second PDCCH candidate at an aggregation level 8, the first PDCCH candidate given by four CCEs numbered 0, 1, 2, 3, the second PDCCH candidate given by eight CCEs numbered 0, 1, 2, 3, 4, 5, 6,
 7. 9. The apparatus of claim 7, wherein the subframe configuration for the first subframe and the second subframe indicates a number of orthogonal frequency division multiplexing (OFDM) symbols used for transmission of downlink channels in the first subframe and the second subframe.
 10. The apparatus of claim 7, wherein a radio network temporary identifier (RNTI) is masked to a cyclic redundancy check (CRC) of the control information.
 11. The apparatus of claim 7, wherein the control information is common control information common to all user equipments in the LAA secondary cell.
 12. The apparatus of claim 7, wherein the processor is configured to activate the LAA secondary cell by receiving an instruction from a primary cell. 